1. Field of Invention
This invention relates to the field of interlocks for preventing the simultaneous operation of plural interrelated devices such as valves and in particular to multi-valve interlocks for permitting the operation of only one of a plurality of valves at any one time.
2. Discussion of the Prior Art
While the advantages of interlocking the operation of a plurality of valves is well known, no interlock design has been disclosed which is characterized simultaneously by low cost, simplicity, ease of maintenance and reliability. The need for providing a multi-valve interlock arises in a variety of situations wherein it is necessary for an operator to regulate the flow of fluid through a plurality of inter-related fluid circuits which could be adversely affected if more than one of the valves were simultaneously moved to an opened or closed position. For example, in tank trucks used for dellivering various types of gasoline and other petroleum products, it is common for the truck to be provided with a separate tank section for each type of petroleum product. In such circumstances, it is necessary to assure that only one unloading valve is opened at a time to prevent air mixing in with the gasoline or other fuel and thereby causing inaccurate measurement of the volume of gasoline actually delivered. One technique for accomplishing this result is disclosed in U.S. Pat. No. 2,185,061 to Meyers wherein a tank truck manifold is disclosed having plural valves including manual operators interlocked by means of a plurality of slidable end-abutting bars whereby the opening of one valve will lock the remaining valves in a closed position. In particular, each valve operator includes a cam finger adapted to be inserted between the abutting ends of a pair of bars whenever the valve is opened to cause the bars on both sides of the cam to be displaced in opposite directions toward the remaining valves to hold these valves closed. A spring biased plunger is reciprocably mounted at the outside ends of the end abutting bars to center the bars when all of the valves are closed.
While useful in many circumstances, devices of the type noted above tend to be complicated and expensive to manufacture. For example, the prior art cam operations require manufacture separate from the valve element and each end abutting bar requires a pair of bearings to constrain the bar for longitudinal movement. Moreover, the centering force applied to the outside ends of the end abutting bars must be very carefully balanced to insure proper alignment of each pair of abutting ends with an associated cam operator. Jamming of the mechanism can thus result should the spring forces become unbalanced with the passage of time.
Other multi-valve interlock systems for use with tank trucks have been disclosed in the prior art such as illustrated in U.S. Pat. No. 2,463,737. Elongated sliding keepers are disclosed which extend between the plural valves in end abutting relationship with keeper ejectors mounted in each valve operator for sliding movement with the keepers when the associated valve is closed and for rotational movement with the operator when the associated valve is being opened. When a valve is opened, the keepers are displaced longitudinally to lock the remaining valves in a closed position. As with other designs known in the prior art, however, each keeper requires a pair of guides which must be individually mounted on the multi-valve unit thereby adding to the expense of providing such an interlock. Moreover, no mechanism is disclosed for automatically biasing the keepers and ejectors to a neutral position and thus a device of this type might render a valve inoperative simply because a keeper has not returned to a neutral position.
Another environment in which a multi-valve interlock is extremely useful is in the operation of internal combustion engine lubrication systems employing plural filter units. Such lubrication systems are often employed on engines which must be operated continuously for long periods of time, thereby necessitating the replacement of worn filter units while the engine is in operation. Large marine engines are usually equipped with this type of lubrication system. If each filter unit were associated with an independently operable shut off valve to block lubrication flow as the filter is being changed (see, for example, U.S. Pat. No. 3,982,520), it would be possible for an operator intentionally or inadvertently to block simultaneously the flow of oil through all filters. Without some sort of interlock between the various valves associated with each filter unit, all filtration of lubrication oil could thus be cut off. This problem is so severe that some marine insurance carriers now require a multi-valve interlock in the lubrication system of any marine engine which they insure. Unfortunately, no multi-valve interlock design has previously been disclosed which simultaneously offers great reliability of operation, simplicity of manufacture and ease of maintenance.